Sunspot

A sunspot is a region on the Sun's surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. Although they are blindingly bright, at temperatures of roughly 5000 K, the contrast with the surrounding material at some 6000 K leaves them clearly visible as dark spots. If they were isolated from the surrounding photosphere they would be brighter than an electric arc.

Sunspot variation

Sunspot numbers have been measured since 1700 AD and estimated back to 11,000 BP. The recent trend is upward from 1900 to 1960s then somewhat downward http://sidc.oma.be/html/wolfaml.html. The Sun was last similarly active over 8,000 years ago.

Related Topics:
1700 - AD - BP - 1900 - 1960s

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The number of sunspots correlates with the intensity of solar radiation. Since sunspots are dark it is natural to assume that more sunspots means less solar radiation. However the surrounding areas are brighter and the overall effect is that more sunspots means a brighter sun. The variation is small (of the order of 0.1%) and was only established once satellite measurements of solar variation became available in the 1980s.

Related Topics:
Solar variation - 1980s

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During the Maunder Minimum there were hardly any sunspots at all and the earth may have cooled by up to 1°C.

Related Topics:
Maunder Minimum - C

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